
public class QuickSort {

    public static void quickSort(int[] arr, int low, int high){
        // low 等于 high时，不需要排序了， 左闭右闭的关系
        if(low < high){
            int pivotIndex = partition(arr, low, high);

            quickSort(arr, low, pivotIndex - 1);
            quickSort(arr, pivotIndex+1, high);
        }
    }

    private static int partition(int[] arr, int low, int high){
        int pivot = arr[high];
        int i = low - 1;

        for(int j = low; j < high; j++){
            if(arr[j] <= pivot){
                i++;
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
        int temp = arr[i+1];
        arr[i + 1] = arr[high];
        arr[high] = temp;
        return  i + 1;
    }

    public static void main(String[] args) {

        int []arr = {10, 7, 8, 9, 1, 5};
        System.out.println("排序前:");
        for(int num: arr){
            System.out.print(num + " ");
        }

        quickSort(arr, 0, arr.length - 1);

        System.out.println("\n排序后: ");
        for(int num: arr){
            System.out.print(num + " ");
        }

    }

}
